Does someone have a working Constellation Junior? (Mychess's one is broken)
And can you try this?

Push white pawn from D4 to D5, does the D5 sensor take longer to register?

Or, same with the queen:
white pawn to E3, black don't care
white queen to G4, black don't care
white queen to G5 **here, sensor response is slow**, black don't care
white queen to G4 **sensor response is slow again**

So, with any vertical 1 square move from 4th to 5th rank, or backwards, the chessboard sensor response is slower than with other moves.

If it happens on the actual chesscomputer too, then it's not a fault in the emulation.